The Eels confirmed on Monday that Dunster had suffered ACL, MCL and PCL ruptures in the 13th-minute incident during Sunday's 26-22 trial loss at CommBank Stadium.
If Fuimaono unsuccessfully challenges the grade-three dangerous contact charge, forgoing the 25 per cent early guilty plea discount, he will miss seven games with loading and carryover points applied.
Cronulla's Braydon Trindall, meanwhile, is facing a two-match suspension — three if he heads to the judiciary and loses — for a grade-two careless high tackle on Thomas Jenkins in the Sharks' 34-6 trial defeat to Penrith.
Trindall was a contender to partner new recruit Nicho Hynes in the halves for the round one clash with Canberra but veteran pivot Matt Moylan is now set to claim the role.
Dunster writhed in pain after the awkward tackle by Fuimaono, who was sent to the sin bin.
Unless exonerated or the charge is downgraded, Fuimaono won't feature in Saturday's Charity Shield clash with South Sydney as players who incur grade-three charges are ineligible for trials.
The 25-year-old's rap sheet includes two previous hip-drop offences in the past two seasons and a reckless high tackle charge for a shot on Melbourne's Ryan Papenhuyzen last year.
Fuimaono was sent off and served five games on the sidelines for the Papenhuyzen incident in Magic Round, as the NRL put its focus on deterring high contact.
Dunster, who was a strong chance to feature in round one, will have surgery in the coming days.
Parramatta said in a statement they are "fully supporting Haze in his efforts to returning to the field in 2023".
His absence is another blow to the Eels' backline depth with Fijian winger Maika Sivo not due back until mid-season as he recovers from an ACL injury while Blake Ferguson has departed.
Former Canberra flyer Bailey Simonsson is all but guaranteed to start on one flank with Sean Russell, Solomone Naiduki and Samuel Loizou options for the other edge.
Young Sharks prop Franklin Pele will receive a one-game ban if he pleads guilty to a shoulder charge on Panthers utility Jaeman Salmon.
Dragons back Tautau Moga has escaped with a fine for a high tackle on Simonsson.
